Pyrolytic processes are known in which waste polymer present in scrap, for example, thermoplastic components, tires, etc., are heated to produce products such as liquid oils, gases, and carbon black. However, there is difficultly in achieving commercial viability for such processes when the yield in recovering aromatic hydrocarbons is low, for example, such that the cost of recovering products is more costly than the cost associated with deriving these materials directly from petroleum.
U.K. Patent No. 1,481,352 discloses a method of thermal decomposition of hydrocarbons by at least partially indirectly contacting the hydrocarbons with a hot gas. The gas is let off after heat exchange separately from the gaseous products formed in the decomposition. Tires are heated in a tube by hot gases flowing through the jacket around the tube. In another embodiment the tube has a grid region to which a combustion gas is fed to aid carbonization by direct gas heating at the grid carbon interface. Steam or CO2 may be fed to the grid to form water gas or reduce gas to aid combustion.
U.S. Bureau of Mines report of investigation #7302 discloses a method of destructive distillation of scrap tires. A report was made of tests conducted under a variety of conditions. Solid, liquid, and gaseous were produced, recovered and analyzed. The quantities of various products were shown to be dependent on test temperature variability in composition of the liquid and gaseous products which changes in temperature was also reported.
U.S. Pat. No. 4,746,406 to Timmann discloses a process for the pyrolytic reprocessing of plastic, rubber, or other hydrocarbon materials in which the resultant pyrolysis gas is brought in a cooling stage to a temperature just above the freezing point of water and to a pressure of approximately 0.8 to 1.4 bar of overpressure. The resultant condensate is then separated and heated to a normal storage temperature and the super atmospheric pressure on the condensate reduced to atmospheric pressure. The gas produced thereby comprising C1 to C4 hydrocarbon compounds is supplied to the pyrolysis process as special product gas. A substantial increase in the proportion of aromatic compounds in the pyrolysis gas is reported.
Although the pyrolytic processes of the prior art can generate reusable products, the resulting yield of useful products can render the process economically unfeasible. The cost of these processes is increased even further when the feed material must be sorted based upon its material composition.